Tin base alloys



United States Patent 3,457,067 TIN BASE ALLOYS Lloyd R. Allen, Belmont, Mass., assignor to National Research Corporation, Newton Highlands, Mass., a corporation of Massachusetts No Drawing. Filed Dec. 2, 1966, Ser. No. 598,611 Int. Cl. C22c 13/00, 1/02 U.S. Cl. 75-175 1 Claim ABSTRACT OF THE DISCLOSURE A tin-base alloy is described which is useful in semiconductive devices such as diodes. The alloy comprises 2-3 percent germanium, 0.1-0.2 percent magnesium.

The invention relates to semiconductive alloys and particularly to tin base alloys, doped with p-type impurities for use in the manufacture of semiconductive devices.

Present semiconductive technology is built around the use of silicon or germanium systems. Both these metals are more expensive and more difllcult to contact than tin. It is known that the grey form (alpha) of tin is semiconductive at low temperatures (e.g. Kendall, B63 Proceedings of the Physical Society, p. 821London, 1950). Yet the industry has rejected the use of tin for semiconductive devices. An objection to tin is that the grey form is unstable at room temperature and readily reverts to the white form (beta). Another objection to the use of tin is that it breaks u in transforming from the white to grey forms.

It is the object of the present invention to provide a grey tin alloy which can be manufactured in useful forms such as wires or ribbons or wafers, etc., is stable at room temperature, and can be doped with desired impurities to change its electrical characteristics.

The invention comprises a new alloy consisting essentially of 2-3 percent by weight germanium, 0.1-0.2 percent by weight magnesium, a dopant impurity, the balance being essentially grey tin. The magnesium generally appears in the form of its oxide although it is originally added to the alloy as an element. The oxide phase is dispersed throughout the alloy and strengthens the material. The magnesium and germanium together are effective to prevent the transformation of grey tin back to white tin at room temperature. It appears that my grey tin alloys can accommodate all the same p-type dopants familiarly used in the silicon and germanium systems,

r 3,457,067 Patented July 22, 1969 (e.g. aluminum, zinc, indium). Only p-type dopants can be used. The grey tin cannot be formed initially when elements constituting n-type dopants (e.g. bismuth, antimony) are added. My grey tin alloys are made by melting the constituents (white tin, germanium, magnesium, dopant) together, casting, extruding, rolling, swa ging, aging, cold working, then exposing to low temperatures to elfect the allotropic transformation of the tin. After this, the alloy can be heated to 45 C., indefinitely, without the tin reverting to the white form. Heating to higher temperatures is also feasible for short periods.

The electrical properties of the semiconductive alloys according to the invention are:

Energy gap .08 electron volts. Conductivity 1.4x 10* ohm m. Electron mobility 0.21 in. /volt-sec. Hole mobility .095 inP/volt-sec.

What is claimed is:

1. As a composition of matter a tin base alloy consisting essentially of about 2-3 weight percent of germanium, about 0.1-0.2 weight percent magnesium, the balance being grey tin, the alloy having a strength in execess of ultimate strength 2000 p.s.i. and particularly characterized by retention of the grey form of tin at elevated temperatures, the alloy having an energy gap of .08 electron volt, a conductivity of l.4 10 ohm mf electron mobility of 0.21 inch per volt-second and hole mobility of .095 inches per volt-sec. and being stable above room temperature.

References Cited UNITED STATES PATENTS 2,504,627 3/1950 Benzer 148-33 X 2,514,879 7/1950 Lark-Horovitz et al. 148-1.5 3,145,842 8/1964 Allen 207l0 3,146,097 8/1964 Allen -175 OTHER REFERENCES Kendall and Ewald, Rev. Phys, vol. 97, 1955 p. 607.

Research and Development of Metals for Low Temperature Applications, PB111453 OTS, April 23, 1954, pp. III-31 thru III34.

CHARLES N. LOVELL, Primary Examiner U.S. Cl. X.R. 25262.3 

